If a capacitor can be built in an insulating substrate, the device as a whole can have a smaller volume than a capacitor made by mounting a chip capacitor on the surface of an insulating substrate and can therefore have a higher density and a smaller size. In addition, the insulating substrate on which an IC is to be mounted can have a lower inductance because a short wire is sufficient to connect the IC with the capacitor, so that noise, e.g., source noise and ground noise, can be greatly diminished. (Refer to JP-B-49-5392, JP-B-53-32233 which corresponds to U.S. Pat. No. 3,617,817, (the term "JP-B" used herein means an examined Japanese patent publications))
Barium titanate and alumina are well known as a conventional ceramic dielectric material and ceramic insulating material, respectively, and are widely used. (Refer to JP-A-60-22346, JP-A-2-141471, and JP-A-3-146466, (the term "JP-A" used herein means an unexamined published Japanese patent application))
However, common ceramic dielectric materials such as, e.g., barium titanate have thermal expansion coefficients of 8.times.10.sup.-6 /.degree. C. or higher, which are considerably high compared with that of semiconductor silicon (IC), and have tensile strengths of about 650 kg/cm.sup.2, which are not satisfactorily high. Hence, although such common ceramic dielectric materials have high dielectric constants and function well when used in a capacitor, they are unsuited for use in combination with an insulating substrate on which an IC is to be mounted. On the other hand, alumina is disadvantageous in that it has a thermal expansion coefficient as high as 6.times.10.sup.-6 to 8.times.10.sup.-6 /.degree.C. and a dielectric constant as low as 10 to 14, although it has a high strength. Therefore, use of alumina as dielectric layers yields capacitors having a small capacity. Thus, there has been no known material which achieves all three properties of thermal expansion coefficient, tensile strength, and dielectric constant. (Refer to U.S. Pat. No. 3,880,493, and 4,408,256)